Method for applying a pattern on to a thermoplastic workpiece and an object produced according to the method

ABSTRACT

The present invention concerns a method for the application of a pattern on a work piece of thermoplastic material, preferably plastic, in which method a material, preferably fabric, carrying a predetermined pattern, is brought into contact against said work piece, that the plastic material is heated to a predetermined temperature, and that said patterned material is allowed to remain in contact with the plastic material for a predetermined time, so that the pattern is completely or partly taken up by the work piece, whereupon said pattern carrying material is removed, a method for the production of an object from the work piece with simultaneous application of the pattern, as well as an object produced according to the method.

The present invention concerns a method for applying a pattern onto awork piece made of thermoplastic material, shaping the work piece tomake an object, as well as an object produced by means of the method.

It is known from U.S. Pat. No. 4,202,663 how to transfer patterns to aobject made of plastic by pacing a polyolefin film between a colourtransfer paper and a sheet of thermoplastic material. Heating takesplace to a sufficient degree for the colour to sublimate through theplastic film and the colour to be absorbed by the plastic sheet withpossible pattern intact. The materials subsequently cool down and areseparated whereby a decorated sheet is made. This colouring methods canalso be used in connection with shaping of objects, so called "in-molddecoration". The disadvantage with this method is that several lastersmust be laid onto the article which is to be patterned and possiblyshaped, and after the process these two layers must on the other hand bediscarded.

The invention concerns more precisely a method, by which an object ofthermoplastic material of the type polyethylene, polypropylene,polystyrene, ABS-plastic etc. is furnished with a pattern at the sametime as a possible shaping of the object takes place.

The property, which makes thermoplastics usable in mans situations, isthe property of these plastics becoming plastic when heated, whichdepends on the forces between the linear macromolecules in the plasticsreducing at elevated temperatures. In this connection the plasticbecomes more or less deformable under pressure. These plastics regaintheir original properties when cooled to normal temperatures. The usualway s to shape these plastics are to vacuum form or press the materialunder pressure into or onto a mould and then let the plastic cool downbefore the mould is taken away.

Thermoplastics are used in man areas where shaping of materials to formobjects is an integral part. In orthopaedic technology different typesof thermoplastics are used to produce rigid objects which are includedin prostheses and other aids, i.e. they are rigid in comparison to softparts made of fabric or another material. The object can e.g. consist ofa brace or the like. The way to produce these objects consists mainly inthat a mould, e.g. made of plaster, is made of the part in question,wherein this mould is individually adjusted to fit the person who willuse the manufactured aid.

Once the mould is produced the object is shaped from some thermoplasticmaterial. e.g. one of the above mentioned plastics. This shaping takesplace through heating up the thermoplastic material to the temperatureat which the material in question can be shaped either through vacuumforming or through the thermoplastic being laid over the preparedplaster mould and being shaped manually.

The above named thermoplastic materials can be obtained either inuncoloured or coloured state. Even if the material is functional and theobjects which arc produced function satisfactorily they often do notgive a completely, satisfactory visual impression. Especially when themanufactured shaped objects are included in orthopaedic aids forchildren it would be desirable to give the objects an aesthetically moreattractive appearance.

It has no surprisingly been shown that through heating up athermoplastic work piece, letting it lie in contact with a patternedfabric, which naturally must withstand temperature received during theheating up without itself being destroyed, the pattern is transferred tothe heated thermoplastic. The thermoplastic work piece in this method ispreferably in the form of a sheet. It is also conceivable to use as thepattern carrying material another heat resistant material withproperties corresponding to those of fabric.

The fabric which during the heating up is brought into contact againstthe sheet shaped plastic material is advantageously made of a stretchmaterial e.g. lycra. The heating up can take place in a press, in whichheat can be applied from both or just one side. In one embodiment thepattern is applied through heating from the side against which thefabric is in contact. i.e. the heat contributes to the pattern on thefabric migrating into the plastic material with the heat.

The reason why the fabric which is used in the method should be made ofa stretch fabric or similarly formable material provided with a patternis that no part of the material provided with a pattern shall moverelative to the plastic during the forming process, i.e. no crease orthe like should arise. The shaping of the sheet shaped plastic workpiece which is heated together with the fabric can e.g. take placethrough the work piece with the fabric being shaped around a plastermould or a mould of another material. With plaster moulds padding can beattached as required to make the manufactured object more comfortable towear. The padding in itself is however not necessary to accomplish themethod itself. The heated, sheet shaped work piece is laid upon thepadding on the face facing away from the mould the material providedwith a pattern is placed with the pattern around the plastic work piece.The plastic work piece is heated to approx. 200° C. or the temperatureappropriate for the respective plastic, so that it can be manuallyshaped around the padded plaster mould with the help of heat-resistantgloves. The plastic is subsequently allowed to cool and stiffen into itsnew shape.

The shaping of the object can also take place by the plastic and thefabric lying in contact with the plastic being fixed in a frame, heatedand placed over a mould, thereafter vacuum is applied and the plastic isshaped around the mould. Subsequently, the plastic is allowed to cooldown.

In the above shaping method the fabric is in contact with thethermoplastic the whole time during shaping and for a determined timeafter shaping. It has been shown that the transferring of the pattern tothe thermoplastic is time dependent, i.e. the longer the time thepattern lies in contact against the plastic, the more of the colour fromthe pattern transfers to the plastic. The amount of penetration into theplastic is also a function of time and possibly also of the heatingtemperature.

Once the desired level of pattern transfer has been reached the fabricis taken away from the shaped part.

A further effect results from the use of the above described stretchmaterial in that a simple structural influence is achieved on theusually shin and smooth plastic material. This means that themanufactured part has an aesthetically attractive appearance and atactually more pleasing surface, partly because of the transferredpattern and partly because the surface of the object is still indeedhard but because of the textured effect it gives a softer impression.

It is of course possible to first give the object made fromthermoplastic its final shape and then bring the deformable patterncarrying material into contact with the shaped object with simultaneousheating and letting the pattern be transferred with the latter process.In this connection, the time and process simplicity advantages which theabove mentioned process permits, namely that the pattern carryingmaterial during the shaping of the object displays a slight adhesion tothe object and thereby a transfers its texture and the pattern point forpoint to the object, are not obtained.

The method according to the invention, which has been described abovewith reference to the described embodiments can, of course be modifiedwithin the frame of the attached patent claims with reference to thedescription.

We claim:
 1. Method for applying a pattern to a thermoplastic workpiece,comprising placing a single sheet of pattern-bearing fabric in directcontact with said workpiece, heating said workpiece at a predeterminedtemperature while allowing said pattern-bearing fabric to remain incontact with said workpiece for a predetermined time to effect transferof said pattern to said workpiece, and removing said fabric from saidworkpiece.
 2. The method according to claim 1, wherein said heating stepis performed with said fabric and said workpiece sandwiched in a press,with heat applied from a side adjacent said fabric.
 3. The methodaccording to claim 1, wherein said thermoplastic workpiece is a plasticmaterial selected from the group consisting of polyethylene,polypropylene, polystyrene and ABS plastic.
 4. The method according toclaim 1, wherein said fabric is a stretch material.
 5. The methodaccording to claim 4, wherein said stretch material is lycra.
 6. Themethod according to claim 1, wherein said thermoplastic workpiece isinitially heated prior to said placing step.
 7. Method for applying apattern to a thermoplastic workpiece, comprising heating said workpiece,placing a single sheet of pattern-bearing material in direct contactwith said heated workpiece, further heating said workpiece and saidmaterial at a predetermined temperature and for a predetermined time toeffect transfer of said patter from said material to said workpiece, andremoving said sheet of material from said workpiece.
 8. The methodaccording to claim 7, further comprising shaping said workpiece to adesired final shape prior to said placing step.
 9. The method accordingto claim 7, wherein said thermoplastic workpiece is a plastic selectedfrom the group consisting of polyethylene, polypropylene, polystyreneand ABS plastic.
 10. The method according to claim 7, wherein saidpredetermined temperature is about 200° C.